Phase II trials almost always see an increase in patient enrollment over phase I trials, according to a recent Cutting Edge Information study.

Oncology Clinical Trials: Drug Development Resources and Case Studies discovered that while not nearly as large as phase III enrollment, phase II trials often require more than 100 patients—and sometimes many more—to complete.

Surveyed pharmaceutical companies revealed phase II trials’ actual enrollments average 121 patients. “Not surprisingly, the actual number of patients enrolled does not equate to the number of planned enrollments,” said Ryan McGuire, research team leader at Cutting Edge Information. “Patient recruitment has always been, and may always be, a key struggle for clinical teams.”

The planned and actual enrollment levels studied range from limited (10 patients) to large (300 patients) for phase II trials. Interestingly, only 43% of pharma companies that provided data hit their goals—demonstrating the difficulties associated with patient enrollment. The data show a relationship between enrollment and costs. Costs steadily increase as the number of patients needed rises (with only a few exceptions). In fact, the correlation coefficient of .86 indicates that patient enrollment is a very strong predictor of phase II total trial costs.

Further breakdown of this data show phase II trials with 100 or fewer patients cost an average of $4.9 million. Trials with 101 to 199 patients cost an average of $7 million. Finally, the cost of trials with more than 200 patients increases tremendously, to an average of $25.7 million.